It is known to provide a 2-stroke marine diesel internal combustion engine marine diesel cylinder with 40 TBN or 70 TBN lubricants containing various additives to reduce wear and improve cleanliness, especially to cylinder liners and piston rings. Often engine operating temperatures and pressures are sufficient to break down the film of the oil of lubricating viscosity on the internal walls of the cylinder, and increased wear and decreased engine cleanliness due to deposits occurs.
Further, typical marine diesel cylinder lubricants are treated at approximately 1.2 to 1.3 g/kW hr. However, marine diesel cylinder lubricants treated at the typical feed rates and higher sulphur fuels often produce higher emissions of SOx (sulphur oxides), NOx (nitrogen oxides) and particulate matter such as soot and oxides of sulphur. With lower sulphur fuels, marine diesel engines may be able to operate with a reduced lubricant feed rate, and reduced emissions of SOx and NOx.
However, due to variations in sulphur content of fuel, the amount of TBN required varies as the amount of base required to neutralise sulphuric acid produced during combustion changes. The presence of excessive amounts of unreacted compounds in an additive package providing TBN, e.g., detergents, can contribute to the formation of deposits. To overcome differences in the sulphur content of fuel, two or more lubricating compositions are independently available for use with differing TBN. One lubricating composition has TBN of 40 to 50 suitable for low sulphur containing fuel, whereas the second lubricating composition has a TBN of 70 or more and is used for higher sulphur containing fuel.
Therefore it would be desirable to have a method of controlling the soot and deposit formation and the amount of TBN required to optimize neutralization of sulphur acids, whilst allowing for variable metering rates of lubricating compositions. The present invention provides such a method.
US Patent Application 2003/0196632 A1 discloses a method to employ instrumentation to effectuate variation in lubricant flow rate in response to actual engine conditions. The method regularly monitors one or more engine parameters with instruments such as XRF or IR for base number measurement. The measured engine parameters are used to calculate the feed rate of lubricant to the engine.
US Patent Application 2003/0159672 A1 discloses a method of regularly monitoring one or more engine parameters of an all-loss lubricating system and calculating from the engine parameters an amount of a secondary fluid that is required to be added to base fluid to create a modified base lubricant that is applied to the engine during operations.
US Patent Application 2003/0183188 A1 discloses a device and a process for real time optimizing engine lubricating oil properties in response to actual operating conditions. The process includes on-line modification of lubricant properties by repeatedly measuring a system that recirculates a base lubricant and one or more system condition parameters at a location of interest. The process then calculates an amount of secondary fluid to add to the lubricant followed by mixing the base fluid with the secondary fluid creating a modified base lubricant and applying to a location of interest.
International Application WO 99/64543 A1 discloses diesel cylinder oil having a viscosity of 15 to 27 mm2/s (or cSt), a viscosity index of at least 95 and a TBN of at least 40 mg KOH/g. The oil is a neutral base stock of no more than 725 SUS viscosity at 100° C. and 2 to 15 wt % of the oil a liquid polyisobutylene with a viscosity of 1500 to 8000 mm2/s (cSt) at 100° C.